1. Field of the Invention
The present invention relates to an image enlargement and reduction processor, more particularly, to an image enlargement and reduction processor used in a picture image processing apparatus, such as a digital copy machine and a facsimile machine, and a method thereof.
2. Description of the Related Art
In a known conventional picture element conversion system, an optical system of a picture image reader is shifted in order to enlarge or reduce a scale of a picture image projected on an image sensor, whereby a picture element density read by the image sensor is converted. Further, in another known picture element conversion system, the picture element density is converted by an electrical method, whereby the picture element density is fixed when reading. As conventional electric methods, a most contiguous picture element substitution method, linear interpolation method, third dimension function convolution method, and so on are known. Among these methods, the known interpolation method has a high image quality. When an interpolation calculation is carried out according to the interpolation method, however, it is necessary to use various kinds of multipliers and dividers, or to use a ROM table.
According to the conventional picture element conversion system in which the optical system of the picture image reader is shifted, the system suffers from disadvantages such that the mechanism of the system is complicated. Also, to obtain enough light intensity in the case of an enlargement projection, it is necessary to make a light intensity of a light source irradiating a paper for reading high requiring a high consumption of electric power. On the other hand, according to another conventional picture element conversion system in which the picture element density is converted by the electrical method, the system suffers from the disadvantages set forth below. Namely, where the electrical system consists of a simple electric circuit, the image quality obtained after the conversion of the picture element density is poor. Further, where the electric system consists of various kinds of multipliers and dividers, the image quality is better but the electric circuit is inevitably large and complicated. Furthermore, where the electric system contains the ROM table, precision of a multiplying factor of the picture element density conversion is restricted in accordance with a capacity of the ROM, and it is substantially impossible to vary the multiplying factor on a fine scale.